Technical Field
The present invention relates to coherent optical detection and, in particular, to optimized normalized least mean square phase estimation in digital coherent receivers.
Description of the Related Art
Coherent detection attracts intensive research because demodulation schemes based in coherent detection can offer high spectral efficiency and high capacity to optical networks, allowing them to meet the demanding bandwidth requirements for exponentially-growing network traffic. In contrast to early coherent detection schemes, current coherent detection resorts to high-speed analog-to-digital converters to sample the detected photocurrents and performs digital signal processing (DSP) algorithms to compensate for transmission impairments and improve system performance. Such digital coherent receivers avoid using costly and complicated optical phase-locked loops, thereby simplifying the structure of optical receivers.
One step in coherent detection is phase estimation. Many coherent detection systems perform phase estimation using discrete step sizes to home in on an accurate value. However, due to changing signal-to-noise ratios, the optimum step size is not constant. These systems therefore suffer from inefficiencies as a result of using suboptimal step sizes.